1. Field of the Invention
The present invention relates to a method of producing a MOS transistor having a salicide (self-aligned silicide) structure.
2. Description of the Related Art
FIGS. 5(a)-5(b) and FIGS. 6(a)-6(c) are sectional views showing a conventional method of producing a MOS transistor having a salicide structure, in the order of steps.
In the case of producing a MOS transistor having a salicide structure by a conventional method, first, a gate oxide film 3 is formed on an active region (-the region free of field oxide film) of a silicon substrate 2 on which a field oxide film 1 has been formed. Then, a gate electrode 7 having a two-layer structure consisting of a polysilicon film 5 and a metal silicide film 6 with a silicon oxide film 4 on top thereof is formed on the gate oxide film 3 (FIG. 5(a)).
Thereafter, a silicon nitride film is built up on the entire surface, and is subjected to anisotropic etching to form a side wall spacer 8 on side walls of the gate electrode 7 (FIG. 5(b)). In this case, those portions of the gate oxide film 3 which are not covered by the gate electrode 7 or the side wall spacer 8 are also etched away, leaving the gate oxide film 9 beneath the gate electrode 7 and the side wall spacer 8.
Thereafter, a diffusion layer 10 is formed in the surface layer of the silicon substrate 2 (FIG. 5(c)).
Then, a metal film consisting of cobalt, titanium or the like is built up on the entire surface, and silicidizing process is carried out to form a metal silicide layer 12 consisting of cobalt silicide (CoSi2), titanium silicide (TiSi2) or the like on the diffusion layer 10 (FIG. 6(a)).
Thereafter, an inter-layer insulation film 14 is formed, and a contact hole 15 overlapping the side wall spacer 8 is formed in the inter-layer insulation film 14 (FIG. 6(b)).
Then, a barrier metal film 16 and a metallic plug 17 are formed in the contact hole 15. Thereafter a metallic wiring 18 is formed on the inter-layer insulation film 14 (FIG. 6 (c)).
In this-manner, a MOS transistor having a salicide structure is produced.
While the method of producing a MOS transistor according to the prior art comprises the above-mentioned steps and the metal silicide layer 12 is formed on the diffusion layer 10 to thereby reduce the resistance of the diffusion layer 10, there is the problem that the resistance of the diffusion layer 10 increases where the width W of the diffusion layer 10 is reduced to or below 0.35 m.
In addition, since the contact hole 15 is formed so as to overlap the side wall spacer 8 by a self-alignment process, the area of contact with the diffusion layer 10 is reduced by the amount of overlap between the contact hole 15 and the side wall spacer 8 and, therefore, there is the problem that the contact resistance is increased.
Accordingly, it is an object of the present invention to provide a method of producing a MOS transistor having a salicide structure in which the resistance of a diffusion layer and contact resistance are low.
A method of producing MOS transistor according to the present invention comprises the steps of: forming a gate electrode on a gate oxide film formed on a silicon substrate, forming a side wall spacer on a side wall of the gate electrode after the formation of the gate electrode, forming a diffusion layer in a surface layer of the silicon substrate after the formation of the side wall spacer, forming a silicon film on the side wall spacer after the formation of the diffusion layer, building up a metal film after the formation of the silicon film and performing a heat treatment to form a metal silicide layer on the diffusion layer and the side wall spacer, and forming an inter-layer insulation film after the formation of the metal silicide layer and providing the inter-layer insulation film with a contact hole overlapping the side wall spacer.
A method of producing MOS transistor according to the present invention is characterized in that the step of forming the silicon film on the side wall spacer comprises a step of sputter etching the exposed surface of the silicon substrate.
A method of producing MOS transistor according to the present invention is characterized in that the amount of etching of the surface of the silicon substrate is not less than 100 xc3x85.
A method of producing MOS transistor according to the present invention is characterized in that the step of forming the silicon film on the side wall spacer comprises the steps of building up a silicon film covering the gate electrode and the side wall spacer, and subjecting the silicon film to anisotropic etching after the building up of the silicon film.